Re: [PATCH v2] KVM/SVM: add support for SEV attestation command

[Paolo Bonzini <pbonzini@redhat.com>]

On 04/01/21 16:17, Brijesh Singh wrote:
> The SEV FW version >= 0.23 added a new command that can be used to query
> the attestation report containing the SHA-256 digest of the guest memory
> encrypted through the KVM_SEV_LAUNCH_UPDATE_{DATA, VMSA} commands and
> sign the report with the Platform Endorsement Key (PEK).
> 
> See the SEV FW API spec section 6.8 for more details.
> 
> Note there already exist a command (KVM_SEV_LAUNCH_MEASURE) that can be
> used to get the SHA-256 digest. The main difference between the
> KVM_SEV_LAUNCH_MEASURE and KVM_SEV_ATTESTATION_REPORT is that the latter
> can be called while the guest is running and the measurement value is
> signed with PEK.
> 
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: John Allen <john.allen@amd.com>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: linux-crypto@vger.kernel.org
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Tested-by: James Bottomley <jejb@linux.ibm.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> v2:
>    * Fix documentation typo
> 
>   .../virt/kvm/amd-memory-encryption.rst        | 21 ++++++
>   arch/x86/kvm/svm/sev.c                        | 71 +++++++++++++++++++
>   drivers/crypto/ccp/sev-dev.c                  |  1 +
>   include/linux/psp-sev.h                       | 17 +++++
>   include/uapi/linux/kvm.h                      |  8 +++
>   5 files changed, 118 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst
> index 09a8f2a34e39..469a6308765b 100644
> --- a/Documentation/virt/kvm/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/amd-memory-encryption.rst
> @@ -263,6 +263,27 @@ Returns: 0 on success, -negative on error
>                   __u32 trans_len;
>           };
>   
> +10. KVM_SEV_GET_ATTESTATION_REPORT
> +----------------------------------
> +
> +The KVM_SEV_GET_ATTESTATION_REPORT command can be used by the hypervisor to query the attestation
> +report containing the SHA-256 digest of the guest memory and VMSA passed through the KVM_SEV_LAUNCH
> +commands and signed with the PEK. The digest returned by the command should match the digest
> +used by the guest owner with the KVM_SEV_LAUNCH_MEASURE.
> +
> +Parameters (in): struct kvm_sev_attestation
> +
> +Returns: 0 on success, -negative on error
> +
> +::
> +
> +        struct kvm_sev_attestation_report {
> +                __u8 mnonce[16];        /* A random mnonce that will be placed in the report */
> +
> +                __u64 uaddr;            /* userspace address where the report should be copied */
> +                __u32 len;
> +        };
> +
>   References
>   ==========
>   
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 566f4d18185b..c4d3ee6be362 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -927,6 +927,74 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   	return ret;
>   }
>   
> +static int sev_get_attestation_report(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	void __user *report = (void __user *)(uintptr_t)argp->data;
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	struct sev_data_attestation_report *data;
> +	struct kvm_sev_attestation_report params;
> +	void __user *p;
> +	void *blob = NULL;
> +	int ret;
> +
> +	if (!sev_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
> +		return -EFAULT;
> +
> +	data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	/* User wants to query the blob length */
> +	if (!params.len)
> +		goto cmd;
> +
> +	p = (void __user *)(uintptr_t)params.uaddr;
> +	if (p) {
> +		if (params.len > SEV_FW_BLOB_MAX_SIZE) {
> +			ret = -EINVAL;
> +			goto e_free;
> +		}
> +
> +		ret = -ENOMEM;
> +		blob = kmalloc(params.len, GFP_KERNEL);
> +		if (!blob)
> +			goto e_free;
> +
> +		data->address = __psp_pa(blob);
> +		data->len = params.len;
> +		memcpy(data->mnonce, params.mnonce, sizeof(params.mnonce));
> +	}
> +cmd:
> +	data->handle = sev->handle;
> +	ret = sev_issue_cmd(kvm, SEV_CMD_ATTESTATION_REPORT, data, &argp->error);
> +	/*
> +	 * If we query the session length, FW responded with expected data.
> +	 */
> +	if (!params.len)
> +		goto done;
> +
> +	if (ret)
> +		goto e_free_blob;
> +
> +	if (blob) {
> +		if (copy_to_user(p, blob, params.len))
> +			ret = -EFAULT;
> +	}
> +
> +done:
> +	params.len = data->len;
> +	if (copy_to_user(report, &params, sizeof(params)))
> +		ret = -EFAULT;
> +e_free_blob:
> +	kfree(blob);
> +e_free:
> +	kfree(data);
> +	return ret;
> +}
> +
>   int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>   {
>   	struct kvm_sev_cmd sev_cmd;
> @@ -971,6 +1039,9 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>   	case KVM_SEV_LAUNCH_SECRET:
>   		r = sev_launch_secret(kvm, &sev_cmd);
>   		break;
> +	case KVM_SEV_GET_ATTESTATION_REPORT:
> +		r = sev_get_attestation_report(kvm, &sev_cmd);
> +		break;
>   	default:
>   		r = -EINVAL;
>   		goto out;
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 476113e12489..cb9b4c4e371e 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -128,6 +128,7 @@ static int sev_cmd_buffer_len(int cmd)
>   	case SEV_CMD_LAUNCH_UPDATE_SECRET:	return sizeof(struct sev_data_launch_secret);
>   	case SEV_CMD_DOWNLOAD_FIRMWARE:		return sizeof(struct sev_data_download_firmware);
>   	case SEV_CMD_GET_ID:			return sizeof(struct sev_data_get_id);
> +	case SEV_CMD_ATTESTATION_REPORT:	return sizeof(struct sev_data_attestation_report);
>   	default:				return 0;
>   	}
>   
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 49d155cd2dfe..b801ead1e2bb 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -66,6 +66,7 @@ enum sev_cmd {
>   	SEV_CMD_LAUNCH_MEASURE		= 0x033,
>   	SEV_CMD_LAUNCH_UPDATE_SECRET	= 0x034,
>   	SEV_CMD_LAUNCH_FINISH		= 0x035,
> +	SEV_CMD_ATTESTATION_REPORT	= 0x036,
>   
>   	/* Guest migration commands (outgoing) */
>   	SEV_CMD_SEND_START		= 0x040,
> @@ -483,6 +484,22 @@ struct sev_data_dbg {
>   	u32 len;				/* In */
>   } __packed;
>   
> +/**
> + * struct sev_data_attestation_report - SEV_ATTESTATION_REPORT command parameters
> + *
> + * @handle: handle of the VM
> + * @mnonce: a random nonce that will be included in the report.
> + * @address: physical address where the report will be copied.
> + * @len: length of the physical buffer.
> + */
> +struct sev_data_attestation_report {
> +	u32 handle;				/* In */
> +	u32 reserved;
> +	u64 address;				/* In */
> +	u8 mnonce[16];				/* In */
> +	u32 len;				/* In/Out */
> +} __packed;
> +
>   #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>   
>   /**
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index ca41220b40b8..d3385f7f08a2 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1585,6 +1585,8 @@ enum sev_cmd_id {
>   	KVM_SEV_DBG_ENCRYPT,
>   	/* Guest certificates commands */
>   	KVM_SEV_CERT_EXPORT,
> +	/* Attestation report */
> +	KVM_SEV_GET_ATTESTATION_REPORT,
>   
>   	KVM_SEV_NR_MAX,
>   };
> @@ -1637,6 +1639,12 @@ struct kvm_sev_dbg {
>   	__u32 len;
>   };
>   
> +struct kvm_sev_attestation_report {
> +	__u8 mnonce[16];
> +	__u64 uaddr;
> +	__u32 len;
> +};
> +
>   #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
>   #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
>   #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)
> 

Queued, thanks.

Paolo